Central to understanding immune mechanisms that control viral responses is a more comprehensive understanding of the depth and breadth of antigen-specific immune responses. This will be particularly important in understanding why in the elderly population there is increased susceptibility to infection and less efficacy in vaccine strategies that are protective in younger cohorts. To study this we propose to apply a novel high-throughput, chip-based cellular microarray to characterize human immune responses during infections/vaccinations. Cellular microarrays are an emerging technology with promising applications in medical diagnostics, vaccine development, treatment of autoimmune diseases, and detection of potential agents of bioterrorism. In this R21 application we will focus specifically on influenza as influenza infections continue to have a major societal impact in terms of high morbidity and mortality, especially in the elderly. Specifically in Aim 1 we propose to demonstrate the efficacy of peptide-loaded HLA-Ig chips to examine both immunodominant and subdominant influenza specific immune responses in CTL expanded in vitro. Once generated and tested on the in vitro expanded cells we will analyze responses from vaccinated volunteers and patients who have documented influenza infection. This will be done for both elderly and younger cohorts to determine differences seen in responding CTL populations. While in this preliminary application the focus will be on the HLA A2 response to influenza, we plan to expand the work proposed here to cover other HLA class I and II alleles as well as other infectious diseases more broadly in the second U01 phase of the application. [unreadable] [unreadable] [unreadable] [unreadable]